The Epidemiology Branch (DESPR) has conducted a case-control study in Illinois and California to determine whether the use of periconceptional vitamin supplements can reduce the risk of neural tube defects. Women having either a fetus or an infant with a neural tube defect have been ascertained through perinatal networks, vital records, and other sources and were matched to two controls on maternal race and geographic locale. One control is a mother with a normal pregnancy, and the other the mother of an infant with a fetus with a major health problem other than a neural tube defect. Cases and controls were interviewed within 3 months of the end of pregnancy to determine whether those having a conceptus with a neural tube defect are less likely to have used vitamins in the periconceptional period. A second major objective was to determine whether or not fertility drug use is associated with neural tube defects. Data on infertility and the use of ovulation-inducing drugs were collected during the same interview. Additional analysis is taking place to look at the descriptive epidemiology of neural tube defects and to explore genetic factors in the etiology of neural tube defects.